Introduction - Strongyloides stercoralis is the smallest nematode known to cause human infection. - It primarily infects the small intestine (duodenum and jeju
Introduction - Strongyloides stercoralis is the smallest nematode known to cause human infection. - It primarily infects the small intestine (duodenum and jejunum) of humans. - Unlike most nematodes, larvae, not eggs, are excreted in feces and detected in stool examination. Life Cycle - Natural host : Humans (also found in dogs and cats). - Infective form : Filariform larva (L3 stage) . - Mode of infection : Skin penetration by L3 larvae , usually through barefoot contact with contaminated soil . - Autoinfection (Internal & External). - Ingestion of contaminated food/water (less common). Types of Development - Direct Development (Parasitic Life Cycle) The rhabditiform larvae (L1) , which hatch from eggs in the intestine, are excreted in feces . - In soil, the larvae molt twice to become the infective filariform larvae (L3) . - These larvae penetrate human skin , enter the venous circulation , travel to the heart and lungs , escape into the alveoli , and migrate to the pharynx , where they are swallowed . - They mature into adult female worms in the small intestine within 15–20 days . - Indirect Development (Free-living Cycle) Rhabditiform larvae (L1) in feces develop into free-living adult males and females in soil . - These free-living worms mate , producing eggs that hatch into new rhabditiform larvae . - These larvae may either:Continue the free-living cycle. - Develop into infective filariform larvae (L3) , which penetrate human skin and initiate the parasitic cycle . - Autoinfection External autoinfection :Some rhabditiform larvae transform into infective L3 larvae while passing through the gut. - These L3 larvae penetrate the perianal skin during defecation , causing perianal creeping eruption (cutaneous larva migrans) . - Internal autoinfection :Occurs inside immunocompromised individuals . - The rhabditiform larvae (L1) mature into filariform larvae (L3) within the intestine . - These L3 penetrate the intestinal mucosa , enter the circulation , and complete their cycle without exiting the body. - This can lead to hyperinfection syndrome , causing systemic complications. Pathogenesis & Clinical Features - Most infections are asymptomatic . - Severe disease occurs in immunocompromised patients . Cutaneous Manifestations - Dermatitis, erythema, and itching at the site of larval penetration. - Allergic responses in previously infected individuals. - Perianal pruritus and urticaria in chronic infections. - Larva currens ("racing larvae"):Rapidly progressing serpiginous urticarial tracks due to migrating larvae. - Starts perianally and spreads rapidly . Pulmonary Manifestations - Occurs during larval migration through the lungs . - Small hemorrhages in alveoli and bronchioles. - Bronchopneumonia , which may progress to chronic bronchitis and asthma-like symptoms . - Strongyloides larvae may be found in sputum . Intestinal Manifestations - Symptoms resemble peptic ulcer disease or malabsorption syndrome . - Mucus diarrhea and abdominal pain. - Severe infections cause honeycombing of intestinal mucosa , leading to sloughing and dysenteric stools . - Complications : Protein-losing enteropathy . - Paralytic ileus . Hyperinfection Syndrome & Disseminated Strongyloidiasis - Occurs in immunocompromised individuals (HIV, chemotherapy, steroids, malnutrition) . - Massive autoinfection leads to filariform larvae entering the arterial circulation . - Larvae may lodge in organs such as the heart, lungs, brain, kidneys, pancreas, liver, and lymph nodes . - Complications : Brain abscess, meningitis, peritonitis . - Septicemia , as larvae carry intestinal bacteria into circulation . Diagnosis 1. Microscopy - Direct stool examination (wet mount) to detect larvae (not eggs) . - Concentration methods (Formol-ether concentration, Baermann's funnel gauze method). Baermann's test : Larvae actively migrate out of feces onto gauze. - Sputum, duodenal aspirates, or jejunal biopsy may also show larvae. 2. Stool Culture - Used when larvae are scanty in stool . - Techniques : Agar plate culture . - Charcoal culture method . 3. Serology - ELISA (95% sensitivity) detects Strongyloides antibodies . - Limitations :Cross-reactivity with other helminths. - Antigens may not always be available. 4. Imaging - X-ray, CT scan, or MRI may help detect intestinal and pulmonary involvement . Treatment & Prophylaxis Treatment - Ivermectin (preferred): 200 µg/kg daily for 2 days . - For disseminated strongyloidiasis , treatment should be extended to at least 5–7 days . - Albendazole ( less effective ): 400 mg daily for 3 days . - Hyperinfection treatment : Ivermectin for 7+ days until larvae disappear from stool/sputum. Prevention & Control Proper disposal of feces to prevent soil contamination. Avoid walking barefoot in endemic areas. Avoid contact with contaminated soil and surface water . Treat all infected individuals to prevent transmission. Screen immunocompromised patients before starting corticosteroids or chemotherapy. Critical Notes & Additional Points Strongyloides stercoralis has a unique free-living cycle , allowing it to persist in the environment. Autoinfection enables lifelong infection if untreated, even in the absence of reinfection. Hyperinfection syndrome has a high mortality rate , especially in HIV/AIDS, transplant patients, and those on immunosuppressants . Unlike most helminths, Strongyloides does not rely on eggs for transmission —diagnosis is based on larval presence in stool . Eosinophilia is a key lab finding, especially in the early stages. Imaging findings in disseminated strongyloidiasis may mimic tuberculosis, pneumonia, or Crohn’s disease .